This invention relates to V-type internal combustion engines having rows of cylinders disposed at an angle to each other.
An internal combustion engine of this kind is disclosed in the German-language periodical Motortechnische Zeitschrift (MTZ) 52 (1991, No. 3), pages 100ff. The so-called VR engine, which is described there and which is mass-produced by the applicant's assignee, includes cylinders grouped in two rows which are set at a comparatively close acute angle to each other. Compared to conventional V-type internal combusion engines having a relatively wide V-angle, this cylinder arrangement has the advantage that it requires only a single cylinder crankcase, with all cylinders contained in one block, and only one cylinder head common to all of the cylinders. Because the two rows of cylinders are offset from each other in the lengthwise direction of the engine, the over-all length of such a VR engine having, for example, six cylinders is only slightly greater than that of a conventional four-cylinder in-line engine, and it has considerably less width than conventional V-6 internal combustion engines.
The cylinder banks of the VR engine are at an angle of 15.degree. with respect to each other, and the three cylinder center-lines of each row of cylinders lied in a common plane, intersecting that of the other row at a spacing of 12.5 mm below the crankshaft. This compact drive results in a further shortening of the engine.
For the geometry of the VR engine crank drive and the crank-shaft crank positions for that engine, as well as the ignition sequences, reference is made to Motortechnische Zeitschrift (MTZ) 51 (1990, No. 10), which describes this VR-engine concept in detail and includes proposals regarding the use of one, two or three camshafts in the common cylinder head to actuate two or four valves each per combustion chamber.
To achieve a maximally compact cylinder arrangement, beside the VR engine already cited, a number of further engine arrangements have been proposed.
Thus, the German-language book Luftgekuhlte Fahrzeugmotoren [Air-cooled vehicle engines], Mackerle-Jehlicka-Moebus-Frank-sche Verlagsbuchhandlung, Stuttgart, page 509, discloses a 16-cylinder engine with an H-shaped cylinder disposition. A compact arrangement is achieved by positioning two 8-cylinder Boxer internal combustion engine one above the other. Each of these engines has its own crankshaft, and the two crankshafts are coupled together to drive a single output shaft. The opposed 4-cylinder rows in each engine are not displaced with respect to each other in the longitudinal direction since the two connecting rods of mutually opposed cylinders have a forked connection on a common crank of the crankshaft.
The same publication, at pages 515ff., discloses another compact engine arrangement in the shape of an X. In this engine, two rows of cylinders are disposed in a V-arrangement which is symmetrical with respect to a vertical plane and all of the cylinders act on a straight crank drive with a common crankshaft. Thus, all of the cylinder axes intersect the central longitudinal axis of the crankshaft. The crankshaft has only four cranks since each crank is acted upon by a main connecting rod and three auxiliary connecting rods. Consequently, the four rows of cylinder have no longitudinal offset with respect to each other.
Another compact arrangement of a plurality of cylinders in an internal combustion engine which is in the shape of a W is disclosed in the German-language periodical sportauto, March 1988, No. 3, pages 90ff. This comparatively wide but short cylinder arrangement has three 4-cylinder rows, a central row being in a vertical plane, and the other two rows being arranged in a V configuration with the first row bisecting the V-angle. These three rows are offset longitudinally with respect to each other, since each crank of the crankshaft has the connecting rods of three cylinders connected to it in side-by-side relation.
One problem with this arrangement is in supplying intake combustion air to the combustion chambers associated with the cylinders uniformly and in removing the exhaust gases since there are inlet passages for only two rows of cylinders in the V-space on one side of the horizontal plane whereas the other side of that V-space must accommodate both the inlet passages associated with one of the rows of cylinders and the outlet passages of the other row of cylinders.
Lastly, Motortechnische Zeitschrift 1940, No. 2, pages 52 and 53, discloses a combination of two V-type internal combustion engines to make a double-V engine with the cylinders arranged so that the bisectors of the angles of the two V-rows, which each have a cylinder angle of 60.degree., make a 90.degree. angle with each other. In this case each of the cylinders is connected to a separate crankshaft.